The present invention relates to a multiband antenna.
In recent years there has been a move towards harmonizing mobile phone systems throughout the world. For Instance, many countries have GSM900 systems enabling users from one country to use their mobile phones in another country. However, this harmonization has not yet been completed. For instance, spectrum availability has lead to the introduction of DCS1800 which is similar to GSM900 but operates in a band In the region of 1800 MHz rather than 900 MHz as in the case of GSM. Additionally, national spectrum management authorities do not necessarily decide to allocate the same bands to the public land mobile network service. For instance, in the United States of America a DCS1SOO-like system (DCS1900) is implemented in a band in the region of 1900 MHz. Further Incompatibilities arise during transitional periods when a new system is being introduced and an old one phased out.
The present invention provides a multiband antenna that is compact.
According to the present invention, there is provided a multiband antenna comprising a doubly resonant slotted substantially planar element having an open-ended slot therein, wherein said element is slotted such that said element has a quarter wave resonance mode at a first frequency and the element has a xc2xe wave resonance mode at a second frequency or the slot has a quarter wave resonance mode at a second frequency, the second frequency not being substantially three time the first frequency. The planar element need not be flat but will have a large area to thickness ratio. For instance, the planar element may be curved to conform to an overriding structural limitation. Furthermore, the planar element may have small auxiliary portions, such as supporting and/or structures
Greater bandwidth may be obtained by including a further doubly resonant, slotted planar element having an open-ended slot therein.
Preferably, said further element is slotted such that said further element has a quarter wave resonance mode at a third frequency and the further element has xc2xe wave resonance mode at a fourth frequency or its slot has a quarter wave resonance mode at a fourth frequency, the fourth frequency not being substantially three time the third frequency, More preferably, the first and third frequencies are sufficiently close to provide a single unbroken usable bandwidth and/or the second and fourth frequencies are sufficiently close to provide a single unbroken usable bandwidth. This gives a broader bandwidth.
Preferably, a feed circuit comprising an elongate signal line extends past the open ends of the or each slot.
Preferably, said planar elements are separated by a non-conductive strip into which said slots open.
Preferably, an antenna according to the present invention includes an insulating substrate, and the or each planar element is on one side of said substrate and said signal line comprises a strip on the other side of the substrate and is aligned with said non-conductive strip.
Preferably, there is a ground connection to the or each slotted planar element.